EXPLANATION OF PLATE XLVI. 



GRYPHAEA MUTABILIS Morton, P- 452 



i. External view of a nearly complete valve. 



Marshalltown clay-marl; near Sivedesboro, (180). 



GRYPHAEA DISSIMILARIS n. sp., P- 453 



3-4. Two views of a nearly complete individual retaining both 

 valves. 



Hornerstoivn marl; near Woodstown, (/<?/). 



'974 



